“I asked the security guard if she was going to charge me to which she said no but I could not leave until I had apologised to the Muslim guard.
That's detention. He claims he was delayed over an hour. If his description was accurate it was most certainly unjustified detention.
Not just my opinion, but the standard for American (dunno about British) law as well-- if a police officer or similarly-empowered government official tells you that you are not free to leave, then you are, by definition, detained.